Composite material leaf springs are known, which springs typically comprise a filler material, for example, glass roving or other filamentary solids, in an organic resin matrix such as thermoplastic or thermosetting plastic. Such springs are shown, for example, in U.S. Pat. Nos. 2,600,843; 2,829,881 and 3,142,598. Known methods of making composite material leaf springs include, for example, filament winding methods, compression molding methods and pultrusion methods.
In the past, composite material leaf springs have been used in automotive vehicle suspension systems with associated hardware to hold the spring accurately in position. Such spring clamping hardware has been fashioned after hardware previously known for use in conjunction with metal leaf springs. In a typical arrangement, the spring is positioned between a clamping plate on one side and the axle or other wheel carrying member on the other side. Often, a second clamping plate or the like is positioned between the spring and the axle to act as a spring seat. Bolts or the like, for example, U-bolts, are used to clamp the clamping plate and spring to the axle. An abrasion resistant pad can be used between the spring and the clamping plate and/or between the spring and the axle (or spring seat). Exemplary clamping hardware for a composite material leaf spring is seen, for example, in U.S. Pat. Nos. 3,968,958; 3,586,307 and 3,541,605.
Known leaf spring clamping hardware has been found inadequate in certain respects for use in conjunction with composite material leaf springs. Specifically, such spring clamping hardware has been found inadequate to hold the spring in a fixed position relative the axle under conditions experienced in ordinary use. More specifically, known spring clamping hardware often has failed to prevent longitudinal movement of the spring, that is, movement of the spring in a direction along its longitudinal axis (which typically is transverse to the longitudinal axis of the axle). While the longitudinal position of the spring could be adequately fixed by providing a hole through the composite material of the leaf spring and bolting the spring to the spring clamping hardware, this presents several disadvantages. Providing the bolt hole in the leaf spring requires additional fabrication time and introduces additional complexity and cost. In addition, the bolt hole significantly weakens the composite material spring, and so the spring must be made larger, heavier and more costly.
Movement of the composite material leaf spring relative the axle or other wheel carrying member in a direction along the longitudinal axis of the leaf spring changes the pivot point of the leaf spring against the axle. Consequently, the spring rate is altered and the spring fails to perform according to design. Moreover, upon flexure of the spring, the compressive and tensile stresses are improperly distributed, which can lead to increased material fatigue and decreased spring life. Moreover, if excessive, such movement can lead to damage to the vehicle powertrain.
A leaf spring clamp suitable for use with a composite synthetic material leaf spring is disclosed in commonly assigned U.S. Pat. No. 4,519,590. Therein a leaf spring clamp is disclosed to comprise a rigid clamp base which forms a channel to jacket the leaf spring, and a resilient insert which is inserted between the leaf spring and the rigid clamp base. The resilient insert fills substantially entirely the space between theleaf spring and the rigid clamp base. It now has been found that displacement of the leaf spring within the clamp, especially large bending displacements of the spring, is impeded disadvantageously by the presence of the insert. In avoiding this problem, however, the resilient insert cannot be eliminated since the leaf spring must be effectively isolated from rigid clamp parts to prevent abrasion and crushing damage to the synthetic material of the spring.
It is an object of the present invention to provide a leaf spring clamp which secures a leaf spring, especially a filament reinforced composite material leaf spring, in position in a suspension system. More particularly, it is an object of the invention to provide an axle clamp which in ordinary use substantially prevents longitudinal movement of the leaf spring, that is, movement of the spring in a direction along its longitudinal axis. Further, it is a particular object of the invention to provide an axle clamp which does not require either damage or dislocation of either the reinforcing filaments or the resin matrix of the leaf spring and, specifically, which does not require a hole through the leaf spring or concavities in the surface of the leaf spring or other complexities in the shape of the leaf spring.